In copending United States patent application Ser. No. 687,741 filed Apr. 19, 1991 (now U.S. Pat. No. 5,198,080) (E437) as a continuation-in-part of United States patent application Ser. No. 535,165 filed Jun. 8, 1990 (Now U.S. Pat. No. 5,122,240), both assigned to the assignee hereof and the disclosures of which are incorporated herein by reference, and corresponding to PCT publication No. WO 91/18830, there is described the production of an aqueous acidified chlorate ion-containing solution for use in a chlorine dioxide generating process. The process involves electrochemical acidification of an aqueous alkali metal salt solution, which preferably comprises sodium chlorate and sodium sulfate, while alkali metal ions are removed from the aqueous solution.
The process preferably is effected in an electrolytic cell comprising a cation-exchange membrane dividing the cell into an anode compartment and a cathode compartment. The aqueous alkali metal salt solution is fed to the anode compartment and alkali metal ions are removed from that compartment to the cathode compartment through the cation-exchange membrane. Hydrogen ions electrolytically-produced in the anode compartment provide acidification to the aqueous alkali metal solution.
One operational difficulty which has been encountered with respect to operation of this procedure was a relatively high cell voltage under typical conditions of operation, using an anolyte comprising about 1 M sodium sesquisulfate and 2 M sodium chlorate, a catholyte of about 5% NaOH and cell operating temperature of about 50.degree. C. An investigation of this phenomenon indicated that the excessive cell voltage can be attributed largely to a membrane ohmic drop.
A search conducted in the facilities of the United States Patent and Trade-Mark Office with respect to the subject matter of this invention located a large variety of patents relating to electrolysis process and identified as follows:
______________________________________ 4,191,619 4,613,416 3,917,521 4,085,016 3,884,777 4,595,469 4,773,975 4,806,215 4,849,073 4,968,394 4,990,228 4,996,098 WO 91/18830 ______________________________________
However, as will become apparent from the description of the invention below, none of this prior art discloses or suggests the present invention.